Cement manufacture



sept l0, 1940.' C. BREERWOOD A 2,214,716

CEMENT MANUFACTURE Filed June 28, 1939 I CRusHgnv RAw MATERmLs BowL vCLAsslFlER .THICKELJ UNPRocEssEo l' BLENmNe DlLuTloN WATER 'DlLunoN WATER THICKENER l TURBO Ml ER x DlLuTloN WATE d FLOTTON 2ND EFFLUENT CENTRIFUGE 2ND 'CENTRIFUGE EFFLUENT i COMBINED l .WASTE PRoDucrs yINVENTOR`-l l l c.H.faREERwooD vATT-ORNE@ Patented Sept. 10, 1940 PATENT OFFICEv 2,214,116 CEMENT MANUFACTURE harles H. Breerwood, Narberth, Pa., assignor to Separation Process Company, Catasauqua, Pa., a corporation of Delaware Application June 28, 1939, Serial No. 281,593 In Great Britain June 30, 1938 12 Claims. `(Cl. 10G- 25) flotation, among other means, are employed in A combination to effect reductions of the proportions of one or more of the constituent minerals of the natural material, whereby the treated material may be utilized as the ultimate raw mar l5 terial mixture desired for burning, the major proportion of the mixture, or the lime-bearing component of a mixture. The invention has particularly to do with aprelixninary removal'of mineral particles of extreme neness, physically 20 undesirable in the remainder of the process and in the ultimate raw material mixturefol1owed by the removal of an undesirable proportion of one or more siliceous minerals, the latterimineral or minerals usually, but not always,'being abundant o5 in the fractions first'removed.

Throughout the specication and claims, the following terms are limited by definition: -Siliceous is used in a 'generic sense to refer to all mineral compounds of silicon; Silica is limited '30 to mineral forms of silicon dioxide, such as' quartz, and silicate to mineral compounds of silicon and aluminum, such as sericite mica, and

also compounds of silicon and magnesium, such as talc.

In my vco-pending application Serial No. 277,- 004, filed June 2, 1939, I have described and claimed a process for the reduction of proportions of fine silicate minerals occurring in argillaceous limestones, marls, chalks and siliceous 4 components of raw material mixtures, the process employing centrifugal sedimentation, among other means. For the beneficiation of the argillaceous limestones, maris and chalks contemplated therein, the present invention may be employed to advantage either to effect a more com- .ple'te reduction of silicate minerals, particularly for the manufacture of special cernents, or to reduce the proportion of the available material that must be treated completely to provide for the cor- '50 rection of the entire supply. Further, the present invention isappropriate to the treatment of other materials, notamenable to correction by the process of said application, from which proportions of silica, silicates, or both, must be removed from particle size fractionscoarser than the low orders of micron sizes. In my co-pending, application Serial No. 281,594 filed June 28, 1939, I have described and claimed a process generally similar to the present invention, of particular advantage in the treatment of materials 5 of the class contemplated herein, but in which the coarser orders of particle size are either largely calcite or largely calcite and silica, i. e., having a high silica ratio, the process offering economies both in grinding the materials to satisfacl0 tory kiln feed neness and in reducing the proportion of the original materials that must be corrected further by froth flotation. The inferior natural raw materials contem plated herein are limited to the class consisting of argillaceous limestones, maris, and chalks in which natural crystallization is so fine, or in which the materials must be ground to such a high degree of iinene'ss to freethe mineral bonds of a suiiicient proportion of the constituent :or constituents occurring invundesirable proportion, that the ground materials contain a substantial proportion. of mineral particles in the lowest ordersof particle size, e. g., less than about 2 to 3 microns. These low orders of particle size 25 may be abundant in silicates, if the latter are present in forms such as kaolin, mica and talc, but in other cases may consist largely of calcite. The class also includes raw materials, of the types described, contaminated by impurities, such as carbonaceous matter and magnesium hydroxide, in the mineral form brucite. In any case, the class is limited to a raw material, or the lime-bearing component of a raw material mixture, containing an excessive proportion of at least one siliceous mineral.

It is among the principal purposes of the invention to correct the proportions and ratios of the mineral sources of the four essential oxides,

silica, iron oxide, alumina and lime, to be com- 40 bined for the formation of cement clinker, especially for the production of modern types of cement, including those of low heat of hydration, resistant to sulphate and chloride solutions, and

of limitedk delayed expansion in concrete. These purposes can best be understood by reference to complex raw materials of the class contemplated,

containing proportions of mineral'sources of the four oxides essential for the ultimate raw material mixture, but in which the minerals are present in incorrect proportions and ratios, together with one or more impurities which should be eliminated, at least in part. Such materials are usually deficient in calcite and silica but contain excessive proportions of total silicon dioxide and of alumina in the form of silicates, and are frequently contaminated by undesirable proportions of magnesian silicates,'carbonaceous matter and soluble alkalies. It is a principal purpose in the treatment of such materials, to correct the proportions and ratios of the useful constituentminerals, by the elimination of quantities of one or more siliceous constituents, and to reduce the proportions of impurities, whereby the treated materials may be utilized as the ultimate mixture or the major proportion of the ultimate mixture, and when the natural composition will permit, to subject only a limited proportion of the available materials to the complete treatment to be described, whereby the treated portion and a portion untreated except for grinding may be recombined to form the desired mixture. It is also a principal purpose to effect the physical correction of the mixture at the same time, and partly by the same steps, Athe physical corrections including both reduction of the materials to satisfactory kiln feed iineness, with relation to -the largest mineral particles in the ultimate mixture, and the elimination, from the portion to be completely processed, of the extremely fine orders of particle size which react more readily in burning to clinker and at lower temperaturesV than the -majority of the particles of the ultimate mixture.

Expressed more fully, the principal purposes are usually to reduce the proportion of alumina, to enable the production of cements .low in tri-calcium aluminate; to reduce the proportion of magnesia, when present in the mineral forms described, a. dangerous impurity or adulterant frequently present in materials of the class contemplated, and to retain the calcite and crystalline or crypto-crystalline forms of silica, such as quartz, flint, chert, etc., either to correct the relation between lime and silica and to increase the silica ratio, .or to change the proportion of at least one silicate mineral constituent at leastto a degreey that Will permit a nal correcton of the ultimate composition, by the addition of correctives such as sand, iron oxide, or both.

If an available material, of the class described, is to serve as the lime-bearing component of a two-component mixture, in which the other component is to be a clay or shale, the purpose is to process the lime-bearing component ordinarily to reduce the proportion of siliceous matter. The siliceous matter to be reduced in proportion may consist of a single mineral but frequently includes various silicates, such as the aluminum silicates, usually kaolin, sericite mica and feldspars, and magnesian silicates such as the magnesian micas and talc. For example, the component may consist largely of calcite but with a proportion of silica so large that the natural material cannot be combined with the available clay or shale. In such a case, the purpose is to reduce the proportion of silica in an economical manner to a degree such that the combination can be made to v provide the desired ultimate mixture, the combi-.

nation sometimes including the addition of a corrective, such as iron oxide.

:mimicY tirely from the treated portion, and -so far as practicable, mineral particles in size ranges less than about 2 microns, and if micaceous matter is present, to eliminate the mica particles up to about 5 or 6 .microns in diameter, because I- be-l lieve that these low orders of 'particle size, and especially the silicates, are eutectic and are over- -burned at the temperatures required to combine the coarser constituents. As theproportion of silicates, when present,` is usually relatively great in the minus 2 micron fraction, and because nascent silica is extremely active, this fraction should be eliminated from the final mixture, to l gether with larger ranges in particle size 6i mica.- ceous matter, if present. Even if these low orders of size are largely calcite, it is preferable to usually considerably reducing the proportion of Q the supply of materials requiring complete treatment. This preliminary removal considerably reduces the amount and capacity of flotation equipment and the quantity of reagents necessary to eiect complete correction. Likewise, this elimination limits the necessary capacity of the thickening or filtering equipment and its operating cost, and also permits de-watering of the products to a greater degree, whereby the slurry may be fed to the kiln with limited Water content, to economize in fuel consumption in burning. and to take the fullest advantage of available kiln capacity.

It is a further purpose `to employ simple but unusual combinations of grinding, centrifugal sedimentation, froth iiotationand blending to effect the above described chemical and physical corrections in a practical and economical manner.

conventional types cf hydraulic classifiers, lack utility for the preliminary removal of the low orders of particle size, principally because even Gravity classification methods, employing the when uneconomical quantities of dispersing agents` are used, the lower limits of separation according to particle size, under favorable conditions, is at least as high as 15 to 20 microns. At the degree of grinding required, for ,most of the materials contemplated herein, a separation or cut within this range would involve -a prohibitive loss of useful constituents, especially losses of ne calcite and silica in particleszes favorable for reaction in burning to clinker, and upon which a disproportionate amount of grinding power has been expended. Specifically, with relation to the material of the example to be given hereinafter, a separationor cut at this range would eliminate at least the major proportion of the free grains of the minerals, i. e., those of the particle size range from which the principal separations are to be made. Further, this practice would require classification and final thickening equipment of impractical size, requiring enormous volumes of water, and the classification is ineiiicient and involves further'losses, due to the trapping of large grains in ne occulesand the incomplete separation of fineparticles from the coarser fractions.

The presence of colloidal matter in the underflow promotes flocculation and limits the degree of dewatering.

The purposes of the invention, and the practice of the method, can best be explained by reference to argillaceous limestones, and particularly the Bluestone or "cement-rock of the Lehigh Valley District of Pennsylvania. This raw material, being the most complex of the materials of the `class described, will serve to illustrate the complete practice of the method, and to show how it may-be applied to best advantage for the beneiiciation of interior materials of simpler composition.

This material may be described as a Jacksonburg limestone, almost invariably, with respect to any type of ultimate cement raw material mixture, decient in calcite; excessive in siliceous matter, but deiicient in mineral forms of silica; excessivein alumina; about satisfactory in iron oxide, but deficient in iron for some types of cement; contaminated with magnesia, ordinarily to a dangerous degree; contaminated by graphitic carbon, probably colloidal, and contaminated with. alkalies, both combined and A soluble.

'I'he limestone selected for the examples is parl ticularly suitable for purposes of illustration, as it is apparently the most diicult to beneflciate in accordance with the practice of the present method, the principal difliculty having'to do with the unusually fine state of natural crystallization, and the wide distribution of the various constituents and the almost complete dispersion of colloidal or near-colloidal graphitic carbon. It is intermediate in composition between limestone -and shale, the color and general appearance more nearly resembling slate, but calcite is the most abundant mineral. The other principal mineral constituents are quartz; mica, mostly of the sericite variety, but magnesian micas, probably phlogopite are believed to be present; talc; kaolin; iron, principally as the hydroxide, llimonite; and dolomite, which contributes a substantial portion of the xnagnesia. 4 The iineness and limited degree of crystallization makeaccurate identification by petrographi'c methods diflicult, the dimculty being increased by the presence and dispersion of the colloidal carbon, but it is believed romanalytical determinations and examinations of related metamorphosed limestones from the same locality, that finely divided clay minerals such as kaolin and talcare present and contribute to the proportions of alumina and magnesia, respectively. Thin sections of the rock reveal distinct layers of fine calcite grains alternating with thin layers of fine scaly and fibrous sericite, There are occasional elongate lenses and elongated isolated grains of quartz. The quartz is widely distributed, usually as fine grains in eX- cess of ten microns in diameter. The carbonaceous matter is dispersed throughout the rock in intimate contact with* the .various constituents, and constitutes about one-half of 1% of the total mineral weight. Total alkalies are usually less than 1%, the normal range of the material in the locality being from 0.4 to 1.5%, depending particularly upon the' proportionV of micaceous matter.

As will.. appear more analyses of the specimens referred to in the examples to be given hereinafter, unsuitable for cement manufacture without substantial correction. The silicaceous matter and alumina are too high, and the proportions of cal-v yfully from the ':iiemicaly this' material isl cite and pure silica (quartz) are too low. In view of the abundance of alumina, correction of the lime-silica ratio by the usual addition of high grade limestone does not result in a mixture suitable for modern highway'cement, for example, and this practice not only involves incomplete correction particularly with relation to alumina, but is enormously expensive because of the lack of reserves of high grade limestones in this producing district. The proportion of alumina also makes the lmaterial impractical, and sometimes useless, for the production of cement of moderate heat of hydration, and as the analysesY will make obvious, additional correctives such as silica and iron oxide cannot be added as correc- 1 tives to produce mixtures suitable for the manufacture of low-heat, and sulphate resisting types of cement. The proportion of alkalies is not dangerous but reductions are obviously desirable. The graphitic carbon is eliminated in burning, but has the disadvantage of contributing substantially to natural flocculation, 'thereby limiting the degree of dewatering.

The elimination of a part o f the mica, together with iine clay minerals believed to be present, 25

particularly kaolin and talc, will correct the relation between lime and total silica, and of more importance will increase the silica ratio, i..e. total silica divided by the sum of alumina and ironI oxide, and will make a useful reduction of magnesia. 'I'his elimination may be carried either to'. a degree such that the proportions of the constituents are satisfactory for a desired ultimate mixture for the manufacture of a commercial cement, or to a degree that will permit nal correction by the addition of correctives, as will appear more fully hereinafter.

In general, the invention comprises reducing the materials by grinding the crushed raw materials, or at least that proportion of them that must be treated by the complete process, at least to a degree that mineral bond breakage is suilicient to release the excessive proportion of the siliceous mineral or minerals, together with proportions of contaminating minerals called "impurities herein, if present, from the remainder of the'constituents. If silicates are present, the grinding is preferably so controlled that substantial proportions of them arel concentrated in the lowest orders of particle size. The composition and physical characteristics of some of the materials of the class contemplated, and especially some of the lime-bearing components, are such that the entire supply must be treated by the complete process. Materials, such as that specifically described, however, require the complete treatment of only a limited proportion of the total supply, and the material may either be divided prior to grinding whereby the proportion requiring completev processing may be ground to a specific degree with relation thereto, or the entire supply may be ground to kiln feed iineness and satisfactory bond breakage conveniently as a single operation, the ground products then being divided Without relation to particle size.

The portion of the original materials requiring no further treatment, except re-combination with Vcorrelated as to the speed of operation and the rate of introduction and dilution of material that.

the lowest orders of particle size are cut and sepau rated as an eilluent. I have discovered that micaceous matter has a relatively low sedimentation rate, the rate being about half that of other mineral particles, of the same maximum diameter, due to the characteristic particle shape, and that advantage of this can be taken not only to accomplish the ultimate removal of these particles without excessive grinding, but principally to avoid unnecessary reduction of calcite and quartz', with consequent losses thereof in the waste product to be described hereinafter. tion or cut is satisfactory for the present purposes at about minus 2 to 3 microns, and it will be understood, for brevity, that reference to particle size fractions minus 2 or 3 microns is intended to include the over-sized mica particles referred to above, when present in the feed to the centrifuge. If soluble alkalies are present in the material fed l to the centrifuge, they are largely carried away in the effluent, as the latter includes all but a small proportion of the water fed to the machine.

I have discovered that centrifugal sedimentation machines of the type commonly employed for de-watering slurries and sometimes for the classication of solids can be operated in a novel manner to make an eicient separation of as small a proportion of the Weight of the feed as the particle size fractions below 2 to 3 microns, such machines being the only practical apparatus that I have discovered capable of separating at such low orders of particle size. Satisfactory machines of this type include the Bird centrifuge,-

disclosed, for example, in Piper Patent No. 1,962,- 461, and the F. L. Smidth & Company centrifuge, disclosed in Vogel-Jorgensen Patent No.

The operation of the centrifugal separator for the purposes contemplated herein, differs essentially from its use in de-watering by the overloadingvof the machine to such a degree that the ilne fractions described are carried away as an eiliuent. By controlling the rate of feeding and the speed of the bowl or drum, and, to a lesser degree, 'the dilution of the feed, particle size fractions as iine as 2 microns and under, can be separated eilivciently, these fractions representing sometimes proportions as low as 5 to 6% of the total weight of the material, and if ne silicates, including micas, are present, this practice effects the removal of a substantial proportion of siliceous matter.

If natural occulation is pronounced, and persistent in the feed to the centrifuge, the separation of .the low orders of particle size is improved by electrophoresis, or dispersing agents may be employed. Although dispersing agents were not used in thel pulp of the example to be described hereinafter, substantial ilocculation is characteristic of such pulps, and I have found-that the dispersion is complete, at least with relation to the particle sizes to be retained, following the introduction and agitation with approximately 2 pounds of calcium lignin sulphonate or sodium lignin sulphonate per ton of solids and that about the same dispersion can be obtained with 1 pound of either agent used with 1 pound of soda ash, as

more particularly described and claimed in my .Patent No. 2,162,525.

The relatively coarser fractions, comprising the centrifuge cake, are then subjected to froth ilotation for the recoveryfof the useful constituent or constituents thereof. In view of the neness of the mineral particles, flotation is preferably, and

usually must be, carried out in a. circuit,usually with cleaning of the concentrate.

Ordinarily, the'separa-v 1f the constituent to be discarded is iargeiy original material, to form the mixture, or the major proportion thereof.

If, however, the materials are deficient in both calcite and silica, but excessive in silicates, the flotation steps may becarried out in accordance with the procedure Adescribed above, and more fully in the said patent, the flotation tailings,-

instead-of forming a second waste product of the process, being subjected to a second particle size classification to separate a line fraction high inl silicates and principally micaceous, from a coarse fraction low in silicates and containing some useful quantities of calcite not recovered in the concentrate, largely due to incomplete bond breakage between the calcite and silica. lThis separation is preferably carried out in a centrifugal separator to avoid losses of useful constituents, as this apparatus can be controlled to make an accurate division between the high silicav ratio and the low silica ratio fractions. The eiiluent of the second centrifuge, together with the eiuent of the first centrifuge, form the waste products of the process. -The cake discharged from the second centrifuge is diluted to proper moisture content and conveyed to the blending silos from which it is vided for, as by adding quantities of sources of y iron oxide, silica, or both.

As an alternative tothe separation of the tailings of the calcite concentration by means of the( second centrifuge, these tailings may be subjected to a second flotation concentration in the presence of a positive ion or cationic lieta-tion reagent to concentrate the free silicates, `especially the mica, in the froth. A satisfactory reagent for the purpose is dodecyl amine hydrochloride, or reagents of similar characteristics,

the reagents useful for the purpose, and the method of their employment in-both stages of flotation, being more fully described and claimed in Breerwood and Williams Patent No. 2,161,011. This alternative may be employed when it is desired to e'ect a greater reduction in total sili- -cates and with an increased recovery of the uscful constituents of the tailings of the first step of notation. In the practice of this alternative, the tailings will be generally equivalent to recovered Product No. 3, but of somewhat higher A silica ratio. The micaceous concentrate will take the place of the second ellluent as a wasteprod uct of the process.

' As a second alternative, but somewhat more expensive to practice, in view of the comparatively high cost of the positive ion reagents, the cake discharged from the first centrifuge may be subjected to froth flotation in a stage-oiling circuiti.

in-the presence of a frothing agent and a positive ion reagent to concentrate the undesirable proportion of the silicate minerals remaining in the cake, the concentrate of this notation being the Waste product of the flotation step, the tailings being the recovered product corresponding to a combination of recovered Products Nos. 2 and 3. The procedure of this step of flotation is more fully described and claimed in Breerwood and Williams Patent No. 2,161,010.

For a better understanding of the invention, reference is made to the accompanying draw` ing, which illustrates the preferred flow diagram for the processing of the argillaceous limestone, or cement-rock, specifically described above, namely Lehigh Valley Bluestone.

Example c The raw material, processed in accordance with the flow diagram illustrated, isone in which recrystallization is so incomplete that extremely fine grinding must be resorted toto free a sufficient proportion of micaceous matter, particu-V larly sericite, and other clay mineralsfand colloidal matter, petrographic examinations of ground specimens having disclosedthat mineral bond breakage is incomplete in the particle size fractions above 20 microns. As will be apparent from the chemical composition to be given in the table hereinafter, this material is below composition in calcium carbonate, excessive in total sil--l icon dioxide, but deficient in mineral silica, excessive in alumina, the silica ratio being too low to permit correction by the addition of high grade limestone for the production of an ultimate mixture satisfactory for modern commercial Portland cement, and much too low for use in the production of the special cement described previously..

The principal objectives in the treatment of this material are to subject, to the complete treatment of the process, as small a proportion of the original material as will correct or permit the correction of the lime-silica ratio, especially by reducing the proportion of alumina by the removal of fine silicates, includingsericite, although 'other desirable eliminations are made, as will appear more fully hereinafter.

YThe material was ground in closed circuit. Grinding of this type of material is preferably accomplished vin a tube mill in closed circuit with a bowlclassiiier, this operation preferablybeing carried out with a heavy circulating load, in order that the materials may be withdrawn .as

soonas the bond breakage is satisfactory, to

avoid unnecessary reduction of calcite to low or- '.dersof particle size, with consequent losses of this constituent in the eliiuent of the centrifuge. The bowl overflow is then thickenedto normal slurry moisture content, usually about 36% water in an apparatus such as a Dorr thickener..vv The thickener underflow i5 divided, one portion forming the unprocessed, or finished Product No. 1, this product comprising a small proportion vof the weight of the original material. The other portion comprising the remainder of the material constituted the feed to the separating Step about to be described.

The n'eness of the ground material, will ap.- pear in a table hereinafter, together with the physical analyses of the products separated therefrom by centrifugal sedimentation.

For the purposes of the example, the material was ground without dispersing agents, the ground product being diluted to 70% water, the dilution preferably being made ,in an apparatus v such as a turbo-mixer to form a uniform suspension andv to provide a constant head, -the diluted material then being fed to a laboratory type F. L.

Smidth & Company centrifuge atl the rate ofabout 17 cubic-feet an hour, the dilution increasy ing to water in the efliuent. The machine was operated at a speed sufl'lcient to produce a separating force of about 1000 times gravity. The purpose of this operation was to separate a fine fraction substantially of 3 microns and under, including micaceous matter in particle sizes about twice that in maximum diameter, but having equivalent sedimentation behavior.

The flneness of the ground material, including both the unprocessed portion and the feed to the centrifuge is that of the Feed and that of` the separated coarse and fine fractions, i. e., the Cake and Eiiluent respectively, are expressed in terms of cumulative percentages of .Weight below maximum sizes in the following table of particle. size distribution:

Physical analyses as percent minus Sizeinmicrons Feed Cake Eiiiuent fectively separated, and it will be understood` that the particles in the effluent in excess of 5 microns in size are largely micaceous. The eliluent also included alarge proportion of the carbonaceous matter. The chemical analyses and the weights of the feed and' separated product will be given in a. table hereinafter.

The centrifuge cake, or coarser fraction, was diluted to approximately 20% dry solids, dilution and suspension preferably being carried out in a tubo-mixer, and subjected to froth flotation in a laboratorytype Fagergren flotation machine in an operation equivalent to a stage-oiling circuit, the operation being similar to that described in my Patent No. 2,144,254. The remainder of the carbonaceous matter was first removed as a concentrate by the addition of 0.3

pound per ton of a well-known alcohol frothingI agent, which may be described as a mixture of branched and Istraight chain aliphaticmonohydric alcohols boiling' between about 152 C. and about 162 C. obtainable along with methanol by the catalytic hydrogenization of carbon oxides. Other frothers, such as crysilic acid and resinates may be used, but usually. increase the weight losses of calcite when the carbonaceous matter is concentrated by flotation. The notation time was 4 minutes. l

'I'he tailings from 'the carbon. concentration were then subjected .to flotation to produce av rougher calcite concentrate and a -siliceous tailing, in the presence of 0.66 pound per ton of a calcite collecting reagent, comprising the sa: ponified waste products of the distillation of impure coconut oilfatty acid, areagent described more fully -in Vogel-Jorgensen application Serial No. 230,342, filed September 16, 1938, and in the presence of. 0.06 pound per ton of resinate used Aas a frother.

This resinate frother was employed as it may readily be diluted in water and controlled accurately in quantity, particularly because of the veryV small quantity required. `The flotation time was 1 minute and 50 seconds;

calcium carbonate content of 84%.

- As an alternative to the concentration of the residual carbonaceous matter, i. e., that remaining in the centrifuge cake,l and not eliminated With'the effluent, the carbonaceous matter may be depressed and rendered substantially harmless by conditioning the pulp, prior to flotation, in the presence of a depressing agent, such as a lignin sulphnate, preferably calcium lignin sulplionate, as more fully described and claimed in my Patent No. 2,130,574. Depression of the residual carbon of the centrifuge' cake can beaccomplished with about 1 pound per ton of calcium lig'nin sulphonate. Although the proportion of carbonaceous matter remaining in the cake is considerably less than 1/2 of 1% of the total mineral weight, it has a tendency to inhibit successful concentration of the calcite. It has natural flotability and especially in the presence of a collecting reagent tends to occulate and thereby 'concentrate a substantial proportion of the various other fine mineral particles, thereby contaminating the flotation concentrates, and involving substantial Weight losses of useful minerals. Further, it has the eifectof adsorbing or otherwise consuming relatively large quantities of fatty acid, or modified fatty acid, collecting reagents. It may be utilized as a part of Product No. 2, or discarded, depending upon the weight and proportions of the other constituents.

The results of the complete processing of the material, as described, are given in the followingtable of chemical analyses, the recovered useful products being numbered as previously described, and in accordance with the drawing, Product No. 2 being a re-combination of the carbon concentrate, Product No. 2a, and the rougher concentrate, Product No. 2b, the percentages of weight referring to the total weight of the original feed, and not to the feed' to each step of separation:

ordinary cement, it will be realized that the proportion of alumina in the mixture isstill too high for the production of improved and special types o'f cement. Accordingly, .the original division would usuallyl involve increasing the relative proportion of the feed to the unprocessed material, whereby high grade silica, such as sand, could be added in increasing quantities, as a corrective to increase the silica ratio. It will be recalled that the material was decient in both calcite and silica .and that ordinarily it is desirable, as in the case of this specific material, because of the cost of high grade limestone in the Lehigh Valley district, to recover as much ofthe calcite as possible, together with free silica, and

'- to make up the remaining deficiency in silica by additions thereof obtained from other sources,

' rather than to discard a proportion of the recovered calcite concentrates. Thus, by increasing the relative proportion of Products Nos. 2 and 3 to the proportion of Product No. l, additions of silica can be made to complete correction of the relation between lime and silica and to increase the silica ratio.

It is to be noted that a substantial reduction in the proportion of silicates was accomplished in the removal of the rst 'eilluent, the first wastev product of the process, as indicated by the in. crease in alumina from 6.44% to 9.86%, and that in the second eiliuent, or second waste product, silicates were the most abundant mineral, as indicated by the proportion of 15.3% alumina. Although the calcite grade of the combined Products Nos. 2 and 3 was 84%, it will be seen that the proportion of magnesium oxide was less than that of the original material, although the proportion of dolomite could be expected-to increase. The actual reduction in magnesia can be attributed to substantial eliminations of magnesian silicates.

From the foregoing example of the treatment Feed r Analyses as per cent No. Products per cent I Weigh Sio rezo. Aho. cao o. cao Mgo m i `1o0.o 14.23 0.89 M4 74.0 40.9 1.9 35.7 1.94

ggg, ggg -gg g3g 58.4 32.6 1.79 37.1 1.59' 2a Carbon concentrate. 2: 6 f l 42 1 1' 76 36' 3 2' 26 l Carbon tailing 84. 8 77 4 2b Rougher concentrata--. 66. 2 88.0

seamen si i5- M e uen 2. 98 15. 3 3 2nd cake 7. 6v 3'27 272 2plus3 76.0 8.44 0.63 3.77 84.0 1.55 1.91

By reference to the foregoing table, it will be seen that the processing ofthe materials was specically arranged -to demonstrate the completetreatment of a minimum-proportion of the original supply. To form an ultimate mixture having a calcium carbonate content of 75.8%, the mixture, -by weight, would comprise 82% of the unprocessed raw material, Product No. 1, the composition of which was identical to that of the feed, as given in the table, and 18% of the combined Products Nos. 2 and 3 .which had'a 'I'he original division of the ground raw material supply would, therefore, be made as 76.4% of the weight to be reserved as the unprocessed Product No. 1, and only 23.6% of the weight to be used as the feed to the separation steps, from which which would be satisfactory for the production of of a complex natural material, it will be apparent how the process may be applied in practice' to the treatment of simpler' materials, containv ing fewer mineral constituents, even though the calcite content may be lower, to a degree that the entire material requires the complete treatment described.

I claim:

1. In a method clinker-in which an available inferior material is utilized, and in which the material is amember of the class consisting of argillaceous limestones; marls and chalks, eachv containing an undesirable proportion of at least one mineral constituent, and which must be ground to such a. high degree of neness to free the mineral bonds of said .imdesirable proportion that the ground material contains a substantial proportion of mineral particles in the low orders of particle size; the improvement which comprises of manufacturing cement,

physically a proportion of particles of the unde grinding the material to a degree sufficient to free and burning the remainder of said material as sirable mineral at least equal to the undesirable proportion, subjecting a slurry of at least a proportion of the material so ground' to centrifugal sedimentation so correlated as to the speed of operation and the rate of introduction and dilution of the material that the low orders of particle size comprising a minor partof the weight of said proportion are cut 'and separated as an eluent, subjecting at least a portion of the coarse'r fractions so separated to froth flotation to separate the undesirable proportion of said constituent from the remainderof said material, and burning the remainder of said material as at least a substantial proportion of the ultimate cement raw material mixture.

2. In a -method of manufacturing cement clinker in which an available inferior material is utilized, and in whichv the material'is a mem.

ber of the class consisting of argillaceous limestones, marls and chalks, each containing an undesirable proportion of atleast one mineral constituent, andwhich must be ground to such a high degree of fineness to free the mineral bonds of said undesirable proportion that the ground material contains a substantial proportion of mineral particles in the low orders of particle size; the improvement which comprises grinding the material to a degree sufficient to free physically a proportion of particles of the undesirable mineral at least equal to the undesirable proportion, the material being removed from .the grinding operation before unnecessary reduction of the useful constituents to low orders of particle size, subjecting a slurry of at least a proportion of the material so ground to centrifugal sedimentationso correlated as to the speed of operation and the rate of introduction and dilution of the material that the low orders of particle size comprising a minor part of the weight vof said proportion are cutand separated as an effluent, subjecting at least a portion o'f the coarser fractions so separated to froth flotation toy separate the undesirable proportion of said constituent from the remainder of said material, and burning the remaindero'f said material as at least a substantial proportion of the ultimate cement raw material mixture.

3. In a method of manufacturing cement clinker in which an available inferior material is utilized, land in which the material .is a member of the class consisting of argillaceous limestones, marls and chalks, each/containing an undesirable proportion of at least one siliceous mineral constituent, and whichmust be ground to such a high degree of iineness to free the mineral bonds of said undesirable proportion of siliceous mineral that the ground material contains a substantial proportion of mineral particles in the low orders of particle size; the improvement which comprises ,grinding the material to a degree suiiicient to free physically a proportion of partlclesvof said siliceous mineral at least equal to said undesirable i-proportion, subjecting a slurry of at least a proportion of the material so ground to centrifugal sedimentation so correlated as to the speed of .rate the undesirablepijoportion of said siliceous constituent from theirexnainder of the material,

4. In' a method of manufacturing cementl clinker in which an available inferior material is utilized, and in which the material' is a member of the class consisting of argillaceous limestones, marls and chalks, each containing an undesirable proportion of at least one siliceous mineral oonstituent, and an impurity which can be released and increased in proportion in the low orders of particle size by grinding the material, and which material must beg round to such a high degree of fineness to` 'free the mineral bonds of said undesirable proportion o f siliceous constituent that the ground material contains a substantial proportion of mineral particles in the low orders of particle size; the improvement which comprises grinding at least a proportion of the mate'rial to a degree sufficient to free physically a proportion of particles of said siliceous mineral at least equal to said undesirable proportion, subjecting a slurry lof the material so ground to centrifugal sedimentation so correlated to the speed of operation and the rate of introduction anddilution of the material that the low orders of particle size comprising a minor part of the Weight of said proportion are cut and separated as an eilluent including a substantial proportion of said impurity, discarding said eluent, subjecting at least a portion of the coarser fractions so separated to froth flotation to separate the 'undesirable portion of said siliceous constituent from the remainder of of the material, and burning said remainder of material as at least a substantial proportion of the ultimate cement raw material mixture.

5. In a method of manufacturing cement clinker in which an availablefinferior material is utilized, and in which the material is a member one silicate mineral constituent which can be released and increased in proportion in the low orders of particle size by grindingthe material,

and which material must be ground to such a high degree of fineness to free the mineral bonds of said undesirable porportion of siliceous matter 'I that the ground material contains a substantial,

proportion of mineral particles in the low orders of particle size; Ithe improvement which comprises grinding atleast a proportion offsaid material to a degree sufficient to free physically a proportion of particles of said siliceous matter at least equal to said undesirable proportion, subjecting a slurry of the material so ground to centrifugal sedimentation so correlated'to the speed of operation and the rate of introduction and dilution of the material. that the low orders of particle size are cut and separated as an eiiluent including ya substantial proportion of said silicate mineral, discarding said effluent, subjecting at least a portion of the coarser fractions so separated to froth flotation toseparate the remainder of said undesirable proportion of siliceous matter from the remainder of thematerial, and burning said remainder of material as at least a substantial proportion of the ultimate cementraw material mixture.

6. In a method Vof manufacturing cemen clinker in which an available inferior material is utilized, and in which the material is a member of the class consisting of argillaceous limestones, marls and chalks, each containing an undesirable proportion of siliceous matter comprising at least Y of particle size; the improvement which comparticle size arel cut and separated as an eiuent I including a substantial proportion of said silicate contains a prises grinding at least a proportion of said material to a degree sufficient to vfree physically a proportion of particles of said siliceous matter at least equal to said undesirable proportion, subjecting a slurry of the material so ground to centrifugal sedimentation so correlated to the speed of operation and the rate of introduction and dilution of the material that the low orders of mineral, discarding said effluent, subjecting at least a portion' of the coarser fractions so separated to froth flotation to separate a calcite concentrate, separating the tailings of flotation into a finer fraction including the remainder of said undesirable proportion of siliceous matter from a coarser fraction, and burning said coarser fraction and said calcite concentrate as at least a substantial proportion of the ultimate cement raw material mixture. v

7. In a methodof 'manufacturing cement clinker in which an available inferior material is utilized, and in which the material is a member of the class consisting of argillaceous limestones, marls and chalks, each containing an undesirable proportion of siliceous matterv comprising at least one silicate mineral constituent which can be released and increased in proportion in the low orders of particle size by grinding the material, and which material must be ground to such a high degree of neness to free the mineral bonds of said undesirable proportion of siliceous matter that the ground material substantial proportion -of mineral particles in the low orders of particle size; the improvement which'comprises grinding at least aproportion of said material toa degree sufficient to free physically a proportion of particles of said siliceous matter at least equal to said undesirable proportion, subjecting a slurry of the material so ground to centrifugal sedimentation so correlated to the speed 'of operation and the rate of introduction and dilution of the'material that the low orders o f particle size are cut and separated as an eiiiuent including a substantial proportion of said silicate mineral, discarding said eflluent, subjecting at least a portion of the coarser fractions so separated to froth flotation to separate a calcite concentrate, subjecting the tailings of flotation to a second stage of centrifugal sedimentation to separate a nner fraction including the remainder of said undesirable proportion of siliceous matter from a coarser fraction, and burning said coarser fraction and said calcite concentrate as at least a substantial proders of particle size by grinding the material, and which material must be ground to such a high degree of neness to free thel mineral bonds p vof said undesirable proportion of silicate mineral that the ground material contains a sub- 5 stantial proportion of mineral particles in the low orders ofV particle size; the improvement which comprises grinding at least a proportion of said material to a degree sufficient to free physically` a proportionl of particles of said silil0' cate mineral at least equal to said undesirable proportion, subjecting a slurry of the material so ground to centrifugal sedimentation so correlated as to the speed of operation and the rate of introduction and dilution of the material that 15 taining a substantial proportion of silica, and 25 burning said coarser fraction and said calcite concentrate as at least a substantial proportion of the ultimate cement raw material mixture.

9. In a method of manufacturing cement clinker in which an available inferior material is utilized, and in which the material is a member of the classconsistng of argillaceous limestones, marls and chalks, each containing a proportion of silica desired for said mixture and an undesirable\proportion-of at least one silicate mineral which can be released and increased in proportion to they other constituents in the low orders of particle size by grinding the material, and which material must be ground to such a high degree of neness to free the mineral bonds n I of said undesirable proportion of silicate mineral ,that the ground material contains a substantial proportion-of mineral particles in the low orders of particle size; the improvement which com' prises grinding at least a proportion of said material to a degree suflicient to free physically a proportion of particles of said silicate mineral at least equal to said undesirable proportion, subjecting a slurry of the material so ground to centrifugal sedimentation so correlated as to the speed of operation andthe rate of intrgduction and dilution ofthe material that the low orders` of particle size are cut and separated as an eiiluent including a substantial proportion of said silicate mineral, discarding 'said effluent, subjecting at least a portion of the coarser fractions so separated to froth flotation lto vseparate a calcite, concentrate, subjecting the tailings of flotation Ato a second stage of centrifugal sedimentation to separate a ner fraction including the remainder of said undesirable proportion .of sillcate mineral from a `coarser fraction containing a substantial proportion of silica, and burning :sol

said coarser fraction and `said calcite concentrate 65 as at least a substantial proportion ofthe ultimate cement raw material mixture.

10. In a method of manufacturing cemen clinker in which an available inferior material is of the class consisting of argillaceous limestones, marls and chalks, each containing an undesirable proportion of at least one mineral constituent which proportion can be removed from a portion f utilized, and in which the material is a member 7o of the vtotal raw material supply, and in which 75 lmy.

cally suitable vfor .material l s 2,214,716 at least, must be groundto auch a said portion, high degree of finenes's to free the mineral bonds of said undesirable proportion that the ground material contains a. substantial proportion of mineral particles in the low orders of micron size; the improvement which comprises grinding at least a sumcient portion of the material to permit removal of said proportion ofundesirable mineral to a degree sufllcient to fr ee Physically a proportion of particles `of said constituent at least equal to the undesirable proportion, subjecting a slurry of the portion so ground to centrifugal sedimentation so correlated as to the speed of operation and the rate of introduction and dilution of the material that the loworders of particle size are cuty and separated as an eilluent, subjecting at least aA portion of the coarser fractions so separated' to froth notation to separate the undesirable proportion of saidconstituent from the remainder 'of said portion, mainder of 'said portion in suitable proportion with the other portion of the raw material supmixture. 11. In a method of manufacturing cement clinker in which an available inferior material is utilized, and in which the material is a member of the class consisting of vargillarzeous limestones, maris and chalks, each containing an undesirable proportion of at least one mineral constituent which proportion can be removed from a portion of the total raw material'supply, and in which said portion, at least, must be ground to such a high degree of iineness to free the mineral bonds of said undesirable proportion that the ground material' contains a substantial proportion of mineral particles inthe low orders of` micron size and the coarser fractions of grinding are physiburning; the improvement which comprises grinding the material to a degree .suitable for burning and suiilcient to free physically in a portion of the total raw material supply a proportion of said constituent at least equal to the undesirable proportion, dividing said portion from the total ground material supply, subjecting a slurry of saidportion to centrifugal sedimentation so correlated as to speed of opera-- tion and rate of introduction and dilution of the that the low orders of'particle size are cut and separated as an eiliuent, subjecting at least a `portion. of thecoarser fractions so separated to froth nota to separate the undesirable proportion of blending the reand burning the blended material as at least' the major proportion of the cement raw material said constituent from the A remainder of said portion, blending the remainder of said portion in suitable proportion with the remainder ofthe ground raw material, and burning the blended material as at least the major proportion of the ultimate cement raw material mixture.

12. In a method of manufacturing cement clinker in which an available inferior material is utilized, and in winch the material is a member of the class consisting of argillaceous limestones, maris and chalks, each containing a proportion of silica desired for said mixture and an undesirable proportion of at least one silicate mineral which can be released and increased in proportion to the other constituents in the low .orders of ,particle size by grinding the materiall and which undesirable proportion of silicate mineral can'be removed from a portion of the total raw material supply,v and in which said proportion, at least, must be ground to such a high degree of iineness to free the bonds of said proportionof silicate mineral, that the ground material contains a substantial proportion of mineral particles in the low orders of particle size and the coarser fractions of grinding are physically suitable for burning; the improvement whichl comprises grinding the material to a degree suitable for burning and sufficient to free physically in a portion of the total raw material supply a proportion lof the silicate mineral at least equal to the undesirable proportion, dividing said proportion from the total ground raw material supply, subjecting a slurry of said portion to centrifugal sedimentation so correlated as to speed of operation and rate of introduction and dilution of the ma- -terial that the orders of particle size minus about 2 to 3 microns are cut and separated as an eilluent including a substantial proportion of said silicate mineral, discarding said eilluent, subjecting at least a portion of the coarser, fractions so separated to froth flotation to separate a calcite concentrate, subjecting the tailings of flotation to a second stage of centrifugal sedimentation to separate a finer fraction including 'the remainder of said undesirable proportion of silicate mineral from a coarser fraction containing a substantial proportion of silica, blending said coarser fraction and said calcite concentrate in desired proportions with the other rportion of the total ground ravvl material supply, and burning the blended material as at least the major proportion of the ultimate cement raw material mixture.

CHARLES H. BnEEawooD. .l 

